Method and apparatus for treatment of high-pressure natural gas streams



p 1954 K. H. HACHMUTH ETAL METHOD AND APPARATUS FOR TREATMENT OFHIGH-PRESSURE NATURAL GAS STREAMS Filed NOV. 5, 1951 2 Sheets-Sheet 1INVENTORS K. H. HACHMUTH RTL. c INTIRE A T TOR/VE'VS Sept. 21, 1954 K.H. HACHMUTH ETAL 2,689,875 METHOD AND APPARATUS FOR TREATMENT OFHIGH-PRESSURE NATURAL GAS STREAMS '2 Sheets-Sheet 2 Filed Nov. 5, 1951INVENTORS K. H. HACHMUTH R.L. MC INTIRE A 7' TORNEVS Patented Sept. 21,1954 METHOD AND APPARATUS FOR TREAT- MENT OF HIGH-PRESSURE NATURAL GASSTREAMS Karl H. Hachmuth and Robert L. McIntire, Bartlesville, kla.,assignors to Phillips Petroleum Company, a corporation of DelawareApplication November 5, 1951, Serial No. 254,918

Claims. (0]. 260-676) This invention relates to a new and useful methodof and apparatus for treatment of gas streams. In one of its morespecific aspects, it relates to dehydration of a high pressure naturalgas stream. In another of its more specific aspects, it relates to theseparation of natural gasoline from said stream.

In gas streams as they are produced at the well, there exists aconsiderable quantity of water, water vapor, condensable hydrocarbonsand normally gaseous hydrocarbons. The temperatures in these wells areusually fairly high, and very little condensation takes place before thegas arrives at the surface of the well. However, when this gas stream ispassed into the transmission lines, which are often operated atsubstantially lower pressures, the condensable components are likely tocondense. The liquid water resulting from this condensation reacts withthe hydrocarbons forming solid hydrates. For instance, when operatingwith natural gas streams in the neighborhood of 2,000 p. s. i., hydrateformation becomes troublesome in normal apparatus at tem peratures of 60F. and lower. These hydrates tend to form on relatively cold surfaces,and are particularly troublesome where the gas stream is passed thoughvalves. Shut downs are often necessary because these valves have beenplugged.

By the various aspects of this invention, one or more of the followingobjects will be obtained.

It is an object of this invention to treat the gas to eliminate theseproblems.

Another object of this invention relates to a method of and apparatusfor dehydrating high pressure natural gas streams.

A still further object of this invention relates to the removal ofcondensable hydrocarbons from a gas stream.

Another important object of this invention relates to a method ofrecovering a dry natural gas and liquid hydrocarbon products from a gasstream by means of a self-refrigerating system.

A further object of this invention relates to recovery of dehydrated gasand natural gasoline from a high pressure well in whichthe gas,following hydrate formation and separation, is further expanded in orderto cool the circulating refrigerant which is utilized in the dehydrationstep.

Still further objects will be apparent to one skilled in the art.

The construction designed to carry out our invention will be hereinafterdescribed together with other features thereof.

This invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, wherein an example of the invention is shown,and wherein:

Figure 1 is a diagrammatic view of an apparatus, constructed inaccordance with the invention, for practicing the improved method; and

Figure 2 is a diagrammatic view of a modified form of this invention.

This invention will be described as applied to the main flow line orpipe which extends from a high pressure gas well but, it will beunderstood that it may be applied to any high pressure gas line.

Referring now to the drawings in detail, in Figure 1, l0 designates thehydrate formation and separation chamber. This vessel contains twozones, a cold zone, or hydrate forming zone H, and a warm zone, orhydrate melting zone I2. The gas stream inlet l3 enters chamber [0 belowthe hydrate forming zone ll, after passing through heat exchange coilsl4 and it, heat exchanger and connecting conduits. Temperature control20 regulates the flow of gasthrough heat exchanger I! so that the feedgas entering column It] will be cooled toa temperature just above thatat which hydrates will form. Bubble caps l8 are provided to permit theflow of gas up into the liquid in the cold zone. In. order to direct thehydrates from it into the conduit I9 baffle 2| is provided. The level ofthe liquid in the hydrate melting zone I2 is regulated by the liquidlevel control 23 which permits the withdrawal of water through line 24.

A liquid level is maintained above tray 43 which contains bubble caps18, the upper level of this liquid being indicated by the dotted line49. Ring 5|, which is'positioned at the level of the conduit leading topump 26, is provided with a bottom plate 52 having perforations 53therein. Bafiie 54 is positioned a short distance above section 52 inorder to provide for turbulent flow through the holes 53.

Bafile 2| functions to direct the flow of gas from bubble caps l3 intothe space between baflle El and conduit l9. Solid hydrates, which areformed in zone II as the gas contacts the refrigerant introduced throughnozzles 3!, fall into the liquid above bubble tray 68, where theydescend until they are picked up by the rising gas bubbles and arecarried into the space between. bafile 2| and conduit l9. Due to thefrothing action produced by the gas, these hydrates and some liquidspill over into conduit l9 and descend therethrough into the liquid inhydrate melting zone 12.

Of course, a small portion of the hydrates may in zone l2. The liquidlevel 49 is maintained by the action of conduit [9 serving as anoverflow pipe. The upper end of conduit is is, of course, above thelevel at which pump 26 takes suction.

The formation of hydrates is brought about in zone H by means of acirculating refrigerant, which is circulated by means of pump 25. Thisrefrigerant is a liquid hydrocarbon product of the process. From thispump the refrigerant flows through pipe 21, into heat exchanger 28, toline 29, from which it is released into chamber H by means of spray head3|. This refrigerant is withdrawn from chamber [I through line 32, therate of circulation being controlled by temperature control 33.Refrigerant is a portion of the hydrocarbons condensed in H).

From chamber H] the hydrocarbon products pass to expansion chamber 34,the liquid hydro carbons passing through conduit 35 and the gaseoushydrocarbon through line 3?. Chamber 3% is provided with packed section35. Positioned at, or near, the expansion chamber 3 3 are expansionvalves 33 and 39. As a result of the expansion and cooling of the gas, afurther liquid hydrocarbon fraction is condensed and goes to the bottomof this chamber. The overhead, or gaseous fraction, passes through lineH into heat exchanger 28. From heat exchanger 28 this gas is passedthrough line 42 into heat exchanger H, and from heat exchanger I!through line 43 into storage 44 or transmission line.

By means of liquid level control 48 the flow of liquid hydrocarbons tostorage through line t! is regulated.

In Figure 2, a modification of the form shown in Figure 1 is illustratedwherein the entering gas lifts the refrigerant to the top of the hydrateformation column and the need for a pump, as used in Figure 1, iseliminated. In this modification the liquid and gaseous separation zoneis designated 60. Included are a hydrate forming zone 6! and a hydratemelting zone 62. From the well, or other high pressure source, the gaspasses through line 03, heat transfer coils S4 and 60, heat exchanger6'5, and connecting conduits, before passing through line 08 into thehydrate forming zone Bl. By-pass 69 is located in line H so that aportion of the feed may be passed around heat exchanger 01. This isnecessary in order that the temperature in line 08 be maintained abovethat at which hydrates will be formed. The amount of feed thus by-passedis controlled by temperature control 12.

The circulating refrigerant for this system is withdrawn from the liquidin the upper'portion of the'separating chamber 00 by means of con duit13. This refrigerant is cooled in heat exchanger M by means of expandedproduct gas, which will be hereinafter described, and returned to thelower part of zone 6| through line '56.

I-Iydrates which are conveyed to the upper por tion of separator 60 bymeans of the gas stream, fall by gravity into hydrate melting zone 02,this flow being aided by means of baiile T1. The hydrates are melted inzone 52 by heat exchange with the hot gas passing through coil 64, andthe water is removed through line '89, this rate of removal beingregulated by interface level control 8i. Gaseous and liquid hydrocarbonproducts from the upper portion of separation zone fill flow throughline 82, and are expanded by means of expansion valve 83 before enteringexpansion chamber 84, said column being provided with packed section 85.The expansion and cooling of the gaseous portion results in anadditional fraction of the gas being condensed. The liquid portion iswithdrawn to gasoline storage 36 through line 8?, said withdrawal beingcontrolled by liquid level control 88. The gaseous fraction, cooled as aresult of this expansion, serves as a refrigerant in heat exchanger M,being conveyed to said heat exchanger by line 89. Said gas is thenpassed to the gas storage 9| or transmission line by means of line 92.As the gas in line 92 is still cool with respect to the entering gas, itis further heat exchanged with the entering gas in heat exchanger 67.

In the operation of our invention, gas is conveyed from the well tochamber iii, Figure 1, through line I5. Generally, this gas isconsiderably above the temperature at which hydrate formation occurs.For this reason, various indirect heat exchange steps are shown.However, this cooling should be continued only to a point near that atwhich hydrates will form. This temperature will depend upon the pressureof the gas, which may vary from a few hundred pounds to several thousandpounds. For instance, at 2,000 p. s. i. hydrates begin to form in theneighborhood of 60 F. That is to say if the temperature of the gasstream, at the pressure at which it issues from the earth, is near thehydrate formation point it will not be necessary to use all the heatexchange steps shown in Figure l.

The natural gas stream enters column it through line I3 and bubbles upthrough the bubble caps l8. In the upper part of chamber it it contactsthe circulating refrigerant, and is cooled so that the hydrates areformed in this region. As a general rule, there will be no appreciablepressure drop as the gas enters this chamber. Condensation that occurswill be the result of the lowered temperature. This reduction intemperature is brought about by means of the circulating refrigeranthereinafter described. Hydrates and hydrocarbons which are condensedcollect in the lower section of cold zone I! and flow therefrom throughconduit is into the hydrate melting zone l2. In zone 52 the hydrates areheat exchanged with the original hydrocarbon stream. This hydrocarbonstream will be warm enough to melt the hydrates formed in the upper partof separator H). The water condensed and that resulting from thedecomposition of the hydrates is removed through line 24. At least aportion of the products from chamber to are introduced into expansionchamber ii -i by means of lines 36 and 31. Here they are expanded untila low temperature is reached, and further condensable hydrocarbons arecollected. The liquid fraction is taken off to storage and the gaseousfraction is also taken off to storage or transmission after beingindirectly heat exchanged with the circulating refrigerant in exchanger28 and the feed gas stream in exchanger ll. As the hydrocarbons in thelower portion of chamber 3% have been cooled as a result of thisexpansion, they are available for further cooling of the original gasstream flowing through coil H5 if this is necessary. The apparatus shownin Figure l is adaptable under a wide variety of operating conditions.For instance, the pressure of the natural gas in the field may varywidely. We now believe, but do not wish to be restricted thereto. thatthis invention will find its widest application when used with naturalgas pressures of 1,500 to 3,500 p. s. i. The temperatures can likewisevary over wide ranges. As the only heating necessary is that required tomelt the hydrates, a temperature a few degrees above that of hydrateforma tion results in practical operation. The expansion in chamber 34is governed by two considerations. The first of these is that it isdesired to keep this gas under a pressure sufficient for transmissionand use without further compression. Such lines normally operate in therange of 600 to 1,400 p. s. i. Secondly the expansion should be greatenough to provide the necessary cooling for the circulating refrigerant.

In order that this invention may be more fully understood, certainillustrative temperatures and pressures will be given. On a natural gasline carrying gas at 2,000 p. s. i. and 100 F. the hydrate formationtemperature will be about 60 13. Then, in the apparatus of Figure 1,this gas will be heat exchanged down to a point just above incipienthydrate formation. At 65 F. this gas enters the column and is allowed tobubble up through the liquid phase and is cooled by contact with aliquid refrigerant supplied at a temperature of 0 F. The circulatedrefrigerant is drawn off above the bubble caps and is cooled in heatexchanger 28 to a temperature of F. by indirect heat exchange with theexpanded gas. The hydrates and liquid hydrocarbons flow into the bottomof separator ill wherein the hydrate is decomposed. The overhead gas isexpanded from the initial 2,000 p. s. i. to 860 p. s. i. and thisresults in a cooling to 50 F. This gas is then cool enough to cool thecirculating refrigerant.

The modification of Figure 2 shows different apparatus for carrying outthe method of our invention. In this modification we have eliminated thenecessity for a refrigerant circulating pump. The gas entering thebottom of column 6| causes the flow of the refrigerant up through thiscolumn. Hydrates formed in this column are also carried upward and, whenthey reach the upper part of the column, fall by gravity into thehydrate melting zone 62. The hydrates are melted by indirect heatexchange with the field gas and the water is withdrawn through line 19.Part of the condensable hydrocarbons are Withdrawn through line i3, andare cooled in heat exchanger !4 before being returned to column 0!through line 16.

Gaseous and liquid hydrocarbons pass into expansion column B l whereinthey are cooled. Expansion valve 83 is located in line 82 in order toprovide for expansion of this hydrocarbon stream. The gaseous fractionpasses through heat ex changers M and 61 to the storage chamber 9! ortransmission line (not shown), while the liquid hydrocarbons pass intogasoline storage through line 81, said liquid hydrocarbon withdrawalbeing controlled by liquid level control 88.

This apparatus can be used for the separation of the same type of gasstreams which are discussed in connection with Figure 1. We have foundthat the temperature in the upper part of separation chamber 60 will bein the range of 30 to 50 F., With 40 F. as an average temperature. Ifthe hydrocarbon products are expanded to about 860 p. s. i., thetemperature in the upper part of column 04 will be about 8 F., and thistemperature will be low enough to cool the circulating refrigerant.

The example temperatures and pressures which are given in connectionwith the operation of Figures 1 and 2 are not to be considered aslimiting conditions but are only set forth in order that this inventionmay be more fully understood.

As many possible embodiments may be made of this invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompany ing drawings is to beinterpreted as illustrative and not in a limiting sense.

We claim:

1. A method for the continuous dehydration and recovery of condensablehydrocarbons of a high pressure natural gas stream comprising coolingsaid stream to a temperature just/above that of hydrate formation;contacting said stream with a hydrocarbon refrigerant cooled solely byexpanded product gas, thereby forming hydrates in the liquid phase;contacting said hydrates indirectly with warm field gas to decompose thehydrates; removing the resultant water; conducting at least a portion ofthe hydrocarbons so treated to an expansion zone and condensing anadditional liquid fraction therein; and separating and removing theresultant gaseous and liquid hydrocarbon streams.

2. A method for the continuous dehydration and recovery of condensablehydrocarbons of a high pressure natural gas stream comprising coolingsaid stream to a temperature just above that of hydrate formation;contacting said stream with a hydrocarbon refrigerant cooled solely byexpanded product gas, thereby forming hydrates in the liquid phase;contacting said hydrates indirectly with warm field gas to decompose thehydrates; removing the resultant water; conducting at least a portion ofthe hydrocarbons so treated to an expansion zone and condensing anadditional'liquid fraction therein; cooling said refrigerant by heatexchange with the expanded gaseous hydrocarbon stream; and separatingand removing the resultant gaseous and liquid hydrocarbon streams.

3. A process for separating liquids from a high pressure natural gasstream including cooling said stream as hereinafter described; conveyingsaid stream to a hydrate forming zone; countercurrently contacting saidstream with a refrigerant, thereby condensing a portion of said streamzone; melting the hydrates by means of indirect heat exchange with saidoriginal stream; removing the resulting liquid water; conducting theliquid and gaseous stream removed from said hydrate forming zone to anexpansion zone in order to condense a further liquid fraction; utilizingthe resultant cooled gaseous hydrocarbon stream to cool the refrigerant;and utilizing the resultant cooled liquid hydrocarbon stream to cool theoriginal natural gas stream.

4. A process for separating liquids from a high pressure natural gasstream including cooling said stream as hereinafter described, conveyingsaid stream to a hydrate forming zone; concurrently contacting saidstream with a refrigerant, thereby condensing a portion of said streamand forming hydrates therein; passing the condensed liquid and hydratesinto a hydrate melting zone; melting the hydrates by means of indirectheat exchange with said original stream; removing the resulting liquidwater; conducting the liquid and gaseous stream removed from saidhydrate forming zone to an expansion zone in order to condense a furtherliquid fraction; utilizing the resultant cooled gaseous hydrocarbonstream to cool the refrigerant; and utilizing the resultant cooledliquid hydrocarbon stream to cool the original natural gas stream.

5. Apparatus for removing water and liquid hydrocarbons from gaseousstreams comprising an elongated upright gas-liquid contacting chamher; ahydrate melting chamber in communication with said contacting chamber; afeed gas conduit communicating with the lower portion of said contactingchamber; a refrigerant supply conduit extending into and communicatingwith said contacting chamber; a heat exchanger in said hydrate meltingchamber; a water removal conduit extending from the lower portion ofsaid hydrate melting chamber; a liquid hydrocarbon removal conduitextending from said hydrate melting chamber from a point above saidwater removal conduit; a gas removal conduit extending from the upperportion of said contacting chamber; and a liquid hydrocarbon conduit extending from said contacting chamber.

6. Apparatus for removing water and liquid hydrocarbons from gaseousstreams comprising an elongated upright gas-liquid contacting chamber; ahydrate melting chamber in communication with said contacting chamber; afeed gas conduit communicating with the lower portion of said contactingchamber; a refrigerant supply conduit extending into and communicatingwith said contacting chamber; a heat exchanger in said hydrate meltingchamber; a water removal conduit extending from the lower portion ofsaid hydrate melting chamber; a liquid hydrocarbon removal conduitextending from said hydrate melting chamber from a point above saidwater removal conduit; a gas removal conduit extending from the upperportion of said contacting chamher; a liquid hydrocarbon conduitextending from said contacting chamber and a heat exchanger connectingsaid conduit with said refrigerant supply conduit.

7. Apparatus for removing water and gasoline from natural gas streamscomprising a closed separating vessel having a hydrate forming zone anda hydrate melting zone; a first conduit extending from said meltingzone; a closed expansion chamber; a first heat exchanger; a secondconduit extending through the melting zone of said separating vessel,said expansion chamber, and communicating through said first heatexchanger with the lower portion of the hydrate forming zone of saidseparating vessel; a third conduit extending from the upper portion ofthe separating vessel to the expansion chamber; a fourth conduitextending from the hydrate melting zone to the expansion chamber; asecond heat exchanger; a fifth conduit extending from the upper portionof the expansion chamber, and communicating through said first andsecond heat exchangers with a product outlet; a sixth conduit extendingfrom the hydrate forming zone to said second heat exchanger; a seventhconduit extending from said second heat exchanger to the top of thehydrate forming zone of said separating vessel; and an eighth conduitextending from the lower portion of the expansion chamber to a productoutlet.

8. Apparatus for removing water and gasoline from natural gas streamscomprising a closed separating vessel having a hydrate forming zone anda hydrate melting zone; a first conduit ex tending from said meltingzone; a closed expansion chamber; a first heat exchanger; a secondconduit extending through the melting zone of said separating vessel,said expansion chamber, and communicating through said first heatexchanger with the lower portion of the hydrate forming zone of saidseparating vessel; a third conduit extending from the upper portion ofthe separating vessel to the expansion chamber; a fourth conduitextending from the hydrate melting zone to the expansion chamber; asecond heat exchanger; a fifth conduit extending from the upper portionof the expansion chamber, and communicating through said first andsecond heat exchangers with a product outlet; a sixth conduit extendingfrom the hydrate forming zone to said second heat exchanger, a pump insaid conduit; a seventh conduit extending from said second heatexchanger to the hydrate forming zone of said separating vessel, and aneighth conduit extending from the lower portion of the expansion chamberto a product outlet.

9. Apparatus for removing water and gasoline from natural gas streamscomprising a closed separating vessel having a hydrate forming zone anda hydrate melting zone; a first conduit extending from said meltingzone; a closed expansion chamber; a first heat exchanger; a secondconduit extending through the melting zone of said separating vessel,said expansion chamber, and communicating through said first heatexchanger with the lower portion of the hydrate forming zone of saidseparating vessel; a third conduit extending from the upper portion ofthe separating vessel to the expansion chamber; a fourth conduitextending from the hydrate melting zone to the expansion chamber; asecond heat exchanger; a fifth conduit extending from the upper portionof the expansion chamber, and communicating through said first andsecond heat exchangers with a product outlet; a sixth conduit extendingfrom the hydrate forming zone to said second heat exchanger; a seventhconduit extending from said second heat exchanger to the lower portionof the hydrate forming zone of said separating vessel; and an eighthconduit extending from the lower portion of the expansion chamber to aproduct outlet.

10. Apparatus for removing water and gasoline from gas streamscomprising a closed separating vessel having a hydrate forming zone anda hydrate melting zone; a first conduit extending from said meltingzone; a closed expansion chamber; a first heat exchanger; a secondconduit extending through the melting zone of said separating vessel,said expansion chamber, and communicating through said first heatexchanger with the lower portion of the hydrate forming zone of saidseparating Vessel; at least one hydrocarbon conduit extending from theseparating vessel to the expansion chamber; a second heat exchanger; athird conduit extending from the upper portion of the expansion chamber,and communicating through said first and second heat exchangers with aproduct outlet; a fourth conduit extending from the hydrate forming zoneto said second heat exchanger; a fifth conduit extending from saidsecond heat exchanger to the hydrate forming zone of said separatingvessel; and a sixth conduit extending from the lower portion of theexpansion chamber to a product outlet.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,198,142 Wade 1- Apr, 23, 1940 2,261,927 Moore et al Nov. 4,1941 2,475,255 Rollman July 5, 1949 2,4955% Roberts Jan. 24, 19502,528,028 Barry Oct. 31, 1950

1. A METHOD FOR THE CONTINUOUS DEHYDRATION AND RECOVERY OF CONDENSABLE HYDROCARBONS OF A HIGH PRESSURE NATURAL GAS STREAM COMPRISING COOLING SAID STREAM TO A TEMPERATURE JUST ABOVE THAT OF HYDRATE FORMATION; CONTACTING SAID STREAM WITH A HYDROCARBON REFRIGERANT EXPANDED PRODUCT GAS, THEREBY FORMING HYDRATES IN THE LIQUID PHASE; CONTACTING SAID HYDRATES INDIRECTLY WITH WARM FIELD GAS TO DECOMPOSE THE HYDRATES; REMOVING THE RESULTANT WATER; CONDUCTING AT LEAST A PORTION OF THE HYDROCARBONS SO TREATED TO AN EXPANSION ZONE AND CONDENSING AN ADDITIONAL LIQUID FRACTION THEREIN; AND SEPARATING AND REMOVING THE RESULTANT GASEOUS AND LIQUID HYDROCARBON STREAMS.
 5. APPARATUS FOR REMOVING WATER AND LIQUID HYDROCARBONS FROM GASEOUS STREAMS COMPRISING AN ELONGATED UPRIGHT GAS-LIQUID CONTACTING CHAMBER; A HYDRATE MELTING CHAMBER IN COMMUNICATION WITH SAID CONTACTING CHAMBER; A FEED GAS CONDUIT COMMUNICATING WITH THE LOWER PORTION OF SAID CONTACTING CHAMBER; A REFRIGERANT SUPPLY CONDUIT EXTENDING INTO AND COMMUNICATING WITH SAID CONTACTING CHAMBER; A HEAT EXCHANGER IN SAID HYDRATE MELTING CHAMBER; A WATER REMOVAL 